ORDER IV. PRISMATIC GLAUBER-SALT. 33 



OBSERVATIONS. 



1. The crystals obtained while the solution of sulphate 

 of soda is cooling, are in most cases lengthened in the di- 

 rection of the edges between M and 7 1 , as in Fig. 55. ; and 

 implanted in the place of the face P. Those which are 

 formed duringp a slow evaporation are solitary, and limited 

 by a greater number of faces, as in the crystal represented 

 in Fig. 56. 



2. The chemical formula of prismatic Glauber-salt is 

 Na 8*2 + 20 Aq. = 19-39 of Soda, 24-85 Sulphuric Acid, 

 and 55-76 Water. It is easily soluble in water, but decom- 

 poses readily on being exposed to the air, and falls into 

 powder. It is thus found in nature ; a variety from Egra, 

 in Bohemia, has yielded to REUSS, 



Sulphate \ < 67'024. 



Carbonate [-of Soda -< 16-333. 



Muriate ) 1 11-000. 



Muriate of Lime 5-643. 



The progress of decomposition of this species is very pecu- 

 liar ; it takes its rise from single points, which enlarge and 

 extend in several directions, while the rest of the crystal 

 remains in its original state : so that the whole takes the 

 appearance of worm-eaten wood. 



It is possible also to obtain crystals of the anhydr&u$ 

 Glauber-salt, if a solution of sulphate of soda be evapo- 

 rated at a temperature above 33 centigr., above 106 

 Fahr. The crystals are prismatic, of the form P. P + . 

 Pr + , similar to Fig. 6. ; more commonly they shew 

 only the pyramid P, Vol. I. Fig. 9., whose angles have not 

 yet been ascertained. They are easily cleavable in the di- 

 rection of Pr + co. Their hardness is = 2-5, their specific 

 gravity = 2-462. They are white and transparent, but 

 become very soon opake, if exposed to a higher tem- 

 perature. 



3. The prismatic Glauber-salt is found in nature accom- 

 panying hexahedral Rock-salt and prismatic Epsom-salt, or 

 as an efflorescence upon the soil and several rocks, also on 

 the shores of salt lakes, and in some mineral springs. 



VOL. II. C 



